1. Field of the Invention
The present invention relates generally to the field of doors on hangars for admitting airplanes, and more specifically to a pair of auxiliary hangar doors for use in conjunction with and located above the center of sliding main hangar doors, for admitting the vertical stabilizer of an airplane tail, the auxiliary hangar doors being spring-biased to an open position, and alternately pushed closed and released to open by bearing assemblies attached to the top of the main hangar doors and riding against the lower edges of the auxiliary hangar doors to oppose the spring biasing so that the main and auxiliary hangar doors open and close in unison.
2. Description of the Prior Art
There have long been structures referred to as hangars for sheltering airplanes and their maintenance crews from the elements. These hangars have necessarily had large doors to permit airplane entry and exit. Sliding doors have been preferred, because hangar doors are so large that a substantial area in front of the hangar would have to be kept clear if they opened out on hinges. A problem has been that the vertical stabilizers of airplane tails extend significantly higher than the rest of the airplane.
Hangars often have peaked roofs which receive the stabilizers at their highest point. However, the slant of the roof toward either side of the front gable wall of a hangar limits the height of the hangar doors to a level at or below the lowest roof elevations at the sides. It is not economical to build hangars for light aircraft which are tall enough for the stabilizer to clear the top of the doorway with the airplane in its normal position. As a result, workers handling airplanes must often struggle to pull the tail portion down while the plane is pushed into the hangar. The inconvenience of this operation is multiplied many times at large and busy airports where airplanes are moved into and out of hangars several times a day. It is almost inevitable that workers will become rushed or careless at some point and permit the stabilizer to strike the hangar door frame, damaging both the airplane and the door frame.
The only prior art attempt to solve this problem appears to be that of Townend, U.S. Pat. No. 4,971,129, issued on Nov. 20, 1990. Townend teaches a pair of hangar doors fitted into the gable end of a hangar having a peaked roof. The top edges of each door and the door frame are angled to follow the line of the roof and form a peak of their own. Each door is hinged along its top edge and is divided into upper and lower panels, the top edge of the lower panel being hingedly connected to the bottom edge of the upper panel and being angled parallel to the upper panel top edge. A motorized beam framework fastened to the inside faces of the panels, causes the upper panel to pivot upward into a horizontal position while the lower panel remains vertically suspended therefrom. The angled mounting of the doors not only permits the door frame to be higher at its center but also causes the doors to separate somewhat as they open. The resulting space between the vertical lower panels is sufficient to receive the vertical stabilizer of an airplane.
A problem with Townend is that an existing hangar would have to be modified very substantially to accommodate the angled doors, and the existing doors discarded at a loss. Even if a hangar were fitted with the Townend doors when built, the doors and their support structures would be complicated and costly. Another problem is that, since the doors swing outward, an additional area in front of the hangar must be kept clear, and thereby loses its utility. Still another problem is that, apart from the open center space for the stabilizer, the Townend doors do not provide as tall an opening as do conventional sliding doors. Finally, a structural defect could cause the heavy, elevated doors to fall on workers and the aircraft.
It is thus an object of the present invention to provide a hangar door arrangement for passing airplane vertical stabilizers, which can be easily and inexpensively added to conventional sliding hangar doors.
It is another object of the present invention to provide such a door arrangement wherein the utility of Tarmac space immediately in front of the hangar is not sacrificed.
It is still another object of the present invention to provide such a door arrangement which is simple in design and reliable.
It is finally an object of the present invention to provide such a door arrangement which offers maximum safety.